Cover plates are generally used on turbomachine wheels, along the upstream and downstream faces of buckets or blades mounted on the wheels. The cover plates often support axially-projecting seals, generally referred to as angel-wings seals, that interact with seal lands on adjacent stationary and/or rotating hardware. These seals are intended to prevent both the ingress of hot gases into the rotor wheelspace radially inward of the buckets or blades, and the egress of the cooler wheelspace air into the hot gas path. The angel-wing seals may be integrally cast with the bucket or blade, or may comprise non-integral, separate plates mechanically assembled along axial faces of the wheel so as to cover one or more root portions of the buckets or blades. Examples of non-integral cover plates formed with integral angel-wing seals are disclosed in, for example, U.S. Pat. No. 6,190,131 and in U.S. Published Application 2010/0232938 A1.
There are occasions, however, when it is desired to utilize bucket or blade designs that are unable to accommodate the usual angel-wing seal configurations. For example, in a short-shank bucket or blade design, the shorter shank portions adjacent the bucket or blade root portions do not provide sufficient room for conventional angel-wing seals which, in many applications, are provided in a double-stacked arrangement with radially-spaced inner and outer seal elements.
There remains a need, therefore, for a unique turbomachine angel-wing seal arrangement conducive to the use of various bucket and blade designs.